1. Field of the Invention
The present invention relates to a casing structure. Priority is claimed on Japanese Patent Application No. 2010-074928, filed Mar. 29, 2010, the content of which is incorporated herein by reference.
2. Background Art
A turbo compressor compressing a gas such as air or a refrigerant gas through the rotation of an impeller and discharging the compressed gas is known. The turbo compressor includes, for example, a motor generating rotation power, an impeller rotated by the rotation power of the motor transmitted thereto, and a pair of gears transmitting the rotation power of the motor to the impeller (for example, refer to Japanese Patent No. 2910472). The motor is disposed inside a motor casing, and the impeller and the pair of gears are both disposed inside one compressor casing. An annular seal member is disposed at the connection portion between the motor casing and the compressor casing so as to keep the air-tightness thereof.
However, since the above-described compressor casing is provided to surround both the impeller and the pair of gears, the shape of the compressor casing is apt be complicated and the external shape thereof is apt to increase in size. Since the process of manufacturing the compressor casing becomes complicated, manufacturing effort and cost increase. For this reason, instead of the compressor casing, a casing structure may be used which connects an impeller casing (a first casing) surrounding an impeller and a gear casing (a second casing) accommodating a pair of gears. Furthermore, in order to keep the air-tightness of the connection portion between the impeller casing and the gear casing, the annular seal member is also disposed in the connection portion. Further, a plurality of screw members (bolts and the like) is used to connect the impeller casing and the gear casing to each other. When using the screw member, a part of the screw member is threaded into an internal space formed by connecting the impeller casing and the gear casing to each other in order to decrease the size of the casing as much as possible.
However, the screw member is disposed at the outside of the seal member in the radial direction due to the general arrangement relationship between the seal member and the screw member in the connection portion. For this reason, there is a concern that a gas inside the internal space (a gas flowing from the impeller) may flow to the outside or a gas may flow from the outside into the internal space through a penetration hole into which the screw member at the internal space side is inserted.
The invention is made in view of such circumstances, and an object thereof is to provide a casing structure capable of preventing an inflow and an outflow of a gas in a connection portion between a first casing and a second casing even when a part of a screw member connecting the first casing and the second casing to each other is threaded from an internal space formed by connecting the casings to each other.